Faculty Bibliography

The integration between molecular biology and clinical practice requires the achievement of fundamental steps to link basic science to diagnosis and management of patients. In the last decade, the study of genetic bases of human diseases has achieved several milestones, and it is now possible to apply the knowledge that stems from the identification of the genetic substrate of diseases to clinical practice. The first step along the process of linking molecular biology to clinical medicine is the identification of the genetic bases of inherited diseases. After this important goal is achieved, it becomes possible to extend research to understand the functional impairments of mutant protein(s) and to link them to clinical manifestations (genotype-phenotype correlation). In genetically heterogeneous diseases, it may be possible to identify locus-specific risk stratification and management algorithms. Finally, the most ambitious step in the study of genetic disease is to discover a novel pharmacological therapy targeted at correcting the inborn defect (locus-specific therapy) or even to 'cure' the DNA abnormality by replacing the defective gene with gene therapy. At present, this curative goal has been successful only for very few diseases. In the field of inherited arrhythmogenic diseases, several genes have been discovered, and genetics is now emerging as a source of information contributing not only to a better diagnosis but also to risk stratification and management of patients. The functional characterization of mutant proteins has opened new perspectives about the possibility of performing gene-specific or mutation-specific therapy. In this chapter, we will briefly summarize the genetic bases of inherited arrhythmogenic conditions and we will point out how the information derived from molecular genetics has influenced the 'optimal use of traditional therapies' and has paved the way to the development of gene-specific therapy

CONTEXT: In long QT syndrome (LQTS), disease severity and response to therapy vary according to the genetic loci. There exists a critical need to devise strategies to expedite genetic analysis. OBJECTIVE: To perform genetic screening in patients with LQTS to determine the yield of genetic testing, as well as the type and the prevalence of mutations. DESIGN, PATIENTS, AND SETTING: We investigated whether the detection of a set of frequently mutated codons in the KCNQ1, KCNH2, and SCN5A genes may translate in a novel strategy for rapid efficient genetic testing of 430 consecutive patients referred to our center between June 1996 and June 2004. The entire coding regions of KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 were screened by denaturing high-performance liquid chromatography and DNA sequencing. The frequency and the type of mutations were defined to identify a set of recurring mutations. A separate cohort of 75 consecutive probands was used as a validation group to quantify prospectively the prevalence of the recurring mutations identified in the primary LQTS population. MAIN OUTCOME MEASURES: Development of a novel approach to LQTS genotyping. RESULTS: We identified 235 different mutations, 138 of which were novel, in 310 (72%) of 430 probands (49% KCNQ1, 39% KCNH2, 10% SCN5A, 1.7% KCNE1, and 0.7% KCNE2). Fifty-eight percent of probands carried nonprivate mutations in 64 codons of KCNQ1, KCNH2, and SCN5A genes. A similar occurrence of mutations at these codons (52%) was confirmed in the prospective cohort of 75 probands and in previously published LQTS cohorts. CONCLUSIONS: We have developed an approach to improve the efficiency of genetic screening for LQTS. This novel method may facilitate wider access to genotyping resulting in better risk stratification and treatment of LQTS patients

BACKGROUND: The role of structural heart disease and sodium channel dysfunction in the induction of electrical instability in Brugada syndrome is still debated. METHODS AND RESULTS: We studied 18 consecutive patients (15 males, 3 females; mean age 42.0+/-12.4 years) with clinical phenotype of Brugada syndrome and normal cardiac structure and function on noninvasive examinations. Clinical presentation was ventricular fibrillation in 7 patients, sustained polymorphic ventricular tachycardia in 7, and syncope in 4. All patients underwent cardiac catheterization, coronary and ventricular angiography, biventricular endomyocardial biopsy, and DNA screening of the SCN5A gene. Biopsy samples were processed for histology, electron microscopy, and molecular screening for viral genomes. Microaneurysms were detected in the right ventricle in 7 patients and also in the left ventricle in 4 of them. Histology showed a prevalent or localized right ventricular myocarditis in 14 patients, with detectable viral genomes in 4; right ventricular cardiomyopathy in 1 patient; and cardiomyopathic changes in 3. Genetic studies identified 4 carriers of SCN5A gene mutations that cause in vitro abnormal function of mutant proteins. In these patients, myocyte cytoplasm degeneration was present at histology, whereas terminal dUTP nick end-labeling assay showed a significant increase of apoptotic myocytes in right and left ventricle versus normal controls (P=0.014 and P=0.013, respectively). CONCLUSIONS: Despite an apparently normal heart at noninvasive evaluation, endomyocardial biopsy detected structural alterations in all 18 patients with Brugada syndrome. Mutations in the SCN5A gene, identified in 4 of the 18 patients, may have induced concealed structural abnormalities of myocardiocytes that accounted for paroxysmal arrhythmic manifestations

INTRODUCTION: Experience in endovascular/endocardial techniques for implanting implantable cardioverter defibrillators in early childhood is limited. Potentially, this type of approach could limit the surgical risk, while increasing ICD therapy efficacy. The safety and feasibility of adopting a complete endovascular/endocardial approach for implanting ICDs is assessed by considering the cases of two young children. METHODS AND RESULTS: Two boys, aged 3 and 6 years, were implanted with ICD for a history of syncope and documented ventricular tachycardia (VT). A complete endovascular/endocardial approach was adopted consisting of positioning a bipolar pacing and sensing lead in the right ventricular (RV) apex with intravascular redundancy forming a loop in the inferior vena cava (IVC), and a caval coil placed in the IVC. Sensing values (7-8 mV), pacing threshold (0.5-0.6 V/0.5 msec), and defibrillation testing (case 1 = 10 J, case 2 = 20 J) were all acceptable. During follow-up, in both cases ICD intervened correctly. In one case, 16 months after implantation, because of change in the IVC coil-active can vector, the IVC coil was effectively repositioned to a more distal position. CONCLUSION: A complete endovascular/endocardial ICD implantation technique in early childhood is both feasible and safe. This approach avoids thoracotomy and ensures ICD therapy efficacy

Here we review the current knowledge about the mutations of the gene encoding the cardiac ryanodine receptor (RyR2) that cause cardiac arrhythmias. Similarities between the mutations identified in the RyR2 gene and those found in the gene RyR1 that cause malignant hyperthermia and central core disease are discussed. In vitro functional characterization of RyR1 and RyR2 mutants is reviewed, with a focus on the contribution that in vitro expression studies have made to our understanding of related human diseases